added AdjustBase, AdjustAdd, Raw_at_obs classes plus helper functions in adjust.py
added AdjustBase, AdjustAdd, Raw_at_obs classes plus helper functions in adjust.py

heistermann/wradlib,kmuehlbauer/wradlib,heistermann/wradlib,wradlib/wradlib,kmuehlbauer/wradlib,wradlib/wradlib